Too High to Drive? A New Pot Breathalyzer Might Be Able to Tell

Measuring a driver’s impairment from marijuana use has been one of the thornier issues surrounding legalization efforts nationwide. While drivers suspected of operating a vehicle under the influence of alcohol can be tested for impairment relatively easily and accurately via a roadside breathalyzer test, stoned drivers present more of a challenge to law enforcement. Mostly, this is because there is no quick way beyond a visual assessment to determine how high someone is. According to NPR, California startup Hound Labs thinks it has a solution: a breathalyzer-style tester that can measure how high is too high.

Advertisement - Continue Reading Below

Currently, drivers arrested under suspicion of driving while high may be subjected to blood or urine tests to determine their sobriety. Trouble is, marijuana’s psychoactive ingredient, THC, can hang around in the body in detectable levels for days or even weeks, long after the buzz has receded. Hound Labs leans on research that suggests a person’s high (and thus, the amount of impairment) is strongest within a two-to-three-hour window after using pot. Also during this period, THC can be detected on a person’s breath. This is the crux of Hound Labs’ development: a breathalyzer sensitive enough to sniff out THC—in picograms, or parts per trillion—which is much more diffuse than alcohol on one’s breath.

Car and Driver

Hound Labs’ device consists of a handheld breathalyzer, a separate cartridge with a mouthpiece for taking breath samples that plugs into it, and a processing unit. After taking a breath sample, the tester loads a cartridge into the processing unit, and a few minutes later, a THC result is available.

Magical though that may seem, it doesn’t quite solve the basic problem that plagues municipalities throughout the country: how to decide what level of THC constitutes an unsafe amount for a driver and can be proved to have caused impairment at the time of arrest. (This isn’t a new issue for C/D; we first tackled the notion in a 1980 test we called Puff, the Dangerous Driver: Is Doping and Driving Safe?) So, while Hound Labs’ test unit can detect whether or not someone used marijuana in the recent past, it remains unclear whether the THC concentrations it finds are or aren’t legal, depending on where you’re pulled over. For example, in Colorado and Washington, the legal limit is defined as five nanograms of THC per milliliter as measured in a driver’s blood. In California, there is no defined legal limit; determining a driver’s impairment is left to the arresting officer. Currently, no municipal or state government has any defined standard for impairment as gauged from a driver’s breath sample.

Advertisement - Continue Reading Below

According to Hound Labs, its breathalyzer is intended to detect recent marijuana use since marijuana’s detection on the breath coincides with what it calls “the peak window of impairment.” That can certainly help police narrow down a driver’s marijuana use to either dangerous or less dangerous timelines, a distinction the company says should reduce false accusations of marijuana impairment because of blood tests that detect old THC in a person’s system. But until a legal limit for breath-based THC levels is defined, this clever portable device won’t add much clarity to the nation’s hazy DUI rules for drugged driving. So, stay paranoid.